仅在另一个组合框选择后显示组合框中的更新值

Question

当我从组合框1中选择项目时，它显示组合框2中的项目。

;当我从组合框中选择1的另一项目也显示以前的结果双方的项目和新的结果在组合框中2

我只是想只显示在组合框中2.新的项目，如我选择应该更新组合框1组合框2中的项目并删除以前的项目。

private void cb_oname_SelectedIndexChanged(object sender, EventArgs e) 
{ 
    SqlConnection sqlConnection = new SqlConnection(@"Data Source=.;Initial Catalog=Pizza Mania;Integrated Security=True"); 
    { 
     SqlCommand sqlCmd2 = new SqlCommand("SELECT Product_category FROM Product2 where Product_Name='"+cb_oname.SelectedItem+"'", sqlConnection); 
     { 
      sqlConnection.Open(); 

      SqlDataReader sqlrdr = sqlCmd2.ExecuteReader(); 

      while (sqlrdr.Read()) 
      { 
       cb_ocat.Items.add(sqlrdr["Product_category"].ToString()); 
       cb_ocat.Update(); 
      } 

      sqlConnection.Close(); 
     } 
    } 
} 

Answer 1

您应该从第一个组合的Items集合中删除selectedindex中的项目。

注意，我也改变了你的代码中使用using语句正确的一次性周围物体和一个参数，而不是你的非常危险的字符串连接

private void cb_oname_SelectedIndexChanged(object sender, EventArgs e) 
{ 
    // Safety check, SelectedIndexChanged is called also when there is 
    // no item selected (see later) 
    if(cb_oname.SelectedIndex < 0) 
     return; 

    using(SqlConnection sqlConnection = new SqlConnection(.....)) 
    using(SqlCommand sqlCmd2 = new SqlCommand(@"SELECT Product_category 
        FROM Product2 WHERE [email protected]", sqlConnection)) 
    { 
     sqlConnection.Open(); 
     sqlCmd2.Parameters.Add("@name", SqlDbType.NVarChar).Value = cb_oname.SelectedItem; 

     using(SqlDataReader sqlrdr = sqlCmd2.ExecuteReader()) 
     { 
      // Clear the previous items list 
      cb_ocat.Items.Clear(); 
      while (sqlrdr.Read()) 
       cb_ocat.Items.Add(sqlrdr["Product_category"].ToString()); 
     } 
    } 
    // Remove from the Items collection, but it is not enough 
    cb_oname.Items.RemoveAt(cb_oname.SelectedIndex); 
    // Set the selectedindex to -1 so the current text in the combo is reset   
    cb_oname.SelectedIndex = -1; 
}